Instead of a conventional internal combustion engine (hereinafter referred to as an engine), an alternative power source is under investigation to be used as a power source of a vehicle in order to reduce environment pollution caused by exhaust gas of the vehicle and to prepare for a shortage of limited petroleum resources.
An electric vehicle is a typical example thereof. An electric vehicle runs a motor using electric energy stored in a battery, and uses a driving force of the motor as an entire or partial power source of the vehicle. Such an electric vehicle may be generally divided into a pure electric vehicle that uses only electric energy of a battery as a power source, and a hybrid electric vehicle (HEV) that is equipped with an internal combustion engine such that the power of the engine may be used for charging the battery and/or driving the vehicle.
In a narrow definition, the term “electric vehicle” may means only a pure electric vehicle for differentiation from the term “hybrid electric vehicle”. However, the term “electric vehicle” in the present specification is used in a broad definition and includes both the pure electric vehicle and hybrid electric vehicles. More specifically, the term “electric vehicle” in the present specification means any vehicle that has at least one battery, and electric energy stored in the battery is used as a driving force of the vehicle.
Regarding such an electric vehicle, research for converting part of a braking force to electric energy and using such obtained electric energy for charging a battery is under investigation. That is, during braking, part of the kinetic energy associated with the speed of the vehicle is used for driving a generator such that both a reduction of kinetic energy (i.e., a reduction of vehicle speed) and generation of electric energy are realized at the same time. Such a method for braking a vehicle is called regenerative braking. During regenerative braking, electric energy may be generated by driving a motor in reverse or driving a separate generator. Such regenerative braking of an electric vehicle may enhance the fuel mileage of the electric vehicle. In the case of a hybrid electric vehicle, production of noxious exhaust gasses may be reduced in addition to enhancing of fuel mileage.
An electric vehicle is also provided with a hydraulic brake system for braking using hydraulic pressure. Hydraulic brakes are used as regenerative braking is usually insufficient for required deceleration. Hydraulic brakes are also used because the regenerative braking force acts only on driven wheels connected to a motor. Application of braking force only on the driven wheels may negatively impact the vehicle's dynamic control.
According to prior methods/apparatuses for controlling regenerative braking, regenerative braking force is simply added to hydraulic braking force that is mechanically introduced by a brake pedal operated by a driver. In addition, such a regenerative braking force is controlled to have a value that has no relationship to a required total braking force and/or actual hydraulic braking force. Therefore, even if a brake pedal is depressed with a constant pressure, the total braking force of a vehicle may suddenly fluctuate according to whether regenerative braking is triggered or not. Accordingly, a driver may feel confused due to undesired deceleration of the vehicle that has little relationship to brake pedal operation.
In order to reduce such a discrepancy between the brake pedal operation of a driver and the actual deceleration of a vehicle, the regenerative braking force is usually controlled to be lower than an available maximum. Such low control of regenerative braking deteriorates energy reclamation rate thereof.
In addition, according to the prior art, an optimal design for braking force distribution between driven and non-driven wheels was difficult because the regenerative braking force acts only on driven wheels.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the background of the invention, and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art that is already known in this country to a person of ordinary skill in the art.